It is known that isobutylene and other isoalkenes, or iso-olefins, produced by hydrocarbon cracking may be reacted with methanol and other C1-C4 lower aliphatic alcohols, or alkanol, over an acidic catalyst to provide methyl tertiary butyl ether (MTBE) or the like. Generally, it is known that asymmetrical ethers having the formula (CH.sub.3).sub.3 C-O-R, where R is a C1-C4 alkyl radical, are particularly useful as octane improvers for liquid fuels, especially gasoline.
MTBE, ethyl t-butyl ether (ETBE), tert-amyl methyl ether (TAME) and isopropyl t-butyl ether (IPTBE) are known to be high octane ethers. The article by J. D. Chase, et al., Oil and Gas Journal, Apr. 9, 1979, discusses the advantages one can achieve by using such materials to enhance gasoline octane. The octane blending number of MTBE when 10% is added to a base fuel (R+O=91) is about 120. For a fuel with a low motor rating (M+O=83) octane, the blending value of MTBE at the 10% level is about 103. On the other hand, for an (R+O) of 95 octane fuel, the blending value of 10% MTBE is about 114.
In recent years, a major development within the petroleum industry has been the discovery of the special catalytic capabilities of a family of zeolite catalyst based upon medium pore size shape selective metallosilicates. Discoveries have been made leading to a series of analogous processes drawn from the catalytic capability of zeolites. Depending upon various conditions of space velocity, temperature and pressure lower oxygenates, such as methanol can be converted in the presence of zeolite type catalyst to olefins which can oligomerize to provide gasoline or distillate or can be converted further to produce aromatics. Recognizing the commonality of the feedstock and product between etherification reactions to produce high octane gasoline and zeolite catalyzed conversion reactions, interest has focused on the applicability of combined processes as an approach to advance the art in the production of high octane gasoline.
It has been discovered that under certain conditions substantial improvements in the art of alkyl tert-alkyl ether production can be realized in a combination or integration of etherification and hydrocarbon conversion processes based upon zeolite type catalysis. In U.S. Pat. Nos. 4,788,365, 4,826,507 and 4,854,939 to M. N. Harandi and H. Owen novel processes are described for carrying out the production of MTBE and TAME wherein unreacted alcohol and light olefin components from the etherification reaction are converted to higher hydrocarbons in contact with zeolite catalyst. These patents are incorporated herein by reference. In these processes the etherification reaction is carried out using C.sub.4 + hydrocarbon feedstream rich in iso-olefins with the subsequent oligomerization of unreacted light olefins. Feedstreams comprising C.sub.3 hydrocarbons are not employed and conversion of light paraffins to higher hydrocarbons is not experienced.
In U.S. Pat. No. 4,754,100 by C. M. Sorensen et al., incorporated herein by reference, an improved process is described for converting propane to higher hydrocarbons such as butanes and C.sub.5 aliphatics over zeolite catalyst by adding a monoolefin to the propane feed. In U.S. Pat. application Ser. No. 210,177, filed Jun. 20, 1988 by C. Sorensen et al., incorporated herein by reference, the conversion of normal butane to propane and gasoline over zeolite catalyst is described. Both of these processes for converting light paraffins employing zeolite catalysis are carried out under conditions of high severity at high pressure.
In U.S. patent application Ser. No. 559,739, filed Jul. 30, 1990, by M. N. Harandi et al., incorporated herein by reference, an invention is disclosed comprising a process integration for converting propane and butane in an isoolefin rich feedstock to higher hydrocarbons and high octane gasoline rich in tertiary alkyl ether. The light paraffins conversion is carried out in contact with ZSM-5 zeolite catalyst under high severity conversion conditions. It is also known, as disclosed in U.S. Pat. No. 4,899,008 to R. La Pierre and R. Morrison and incorporated herein by reference, that under the high severity conversion conditions representative of those employed in light paraffins conversion, alkylation of aromatics can be carried out using C.sub.2 -C.sub.4 paraffins as alkylating agents.
It is an object of the present invention to provide an integrated process for the conversion of light paraffins and olefins to tertiary alkyl ethers, higher hydrocarbons, and alkylated aromatics.
Another object of the present invention is to provide a process for the utilization of C.sub.3 + hydrocarbon feedstreams for the production of tertiary alkyl ether rich gasoline and the conversion of C.sub.3 paraffins and olefins to higher hydrocarbons and alkylated aromatics rich gasoline.
Another object of the invention is to reduce benzene in the gasoline pool by alkylating a benzene-rich stream with at least a fraction of the unconverted C.sub.4 's from an MTBE unit.
Yet a further object of the present invention is to provide a process for converting C.sub.3 + feedstock to MTBE rich C.sub.5 + gasoline while converting light paraffins to alkylated aromatics rich gasoline.